Refrigeration system with sublimator



Aug 3, 1965 G. c. RANNl-:NBERG ETAL 3,197,973

REFRIGERATION SYSTEM WITH SUBLIMATOR Filed oct. 14, 1964 United States Patent O 3,197,973 REFRIGERATION SYSTEM WITH SUBLIMATOR George C. Rannenberg, East Granby, and Rafael R.A

This invention relates to refrigeration systems and particularly to a refrigeration system utilizing a sublimator for cooling the refrigerant.

U.S. application Serial No. 303,382 filed on August 20, 1963 now issued as Patent No. 3,170,303 and assigned to the same assignee, discloses and claims a sublimator constructed with a porous member having one surface subjected to an extremely low pressure whichpressure is below the triple point of liquid retained adjacent to the other side of the plate. The liquid passing through the pores in the porous plate migrate to the outer surface by capillary action and upon seeing the low pressure immediately freezes adjacent to and/or within the porous plate. When heat is added, the frozen liquid sublimates directly to space and replacement liquid tending to migrate to the outer surface freezes in a like manner in a continuous cycle. Such a device is self-regulating and eliminates the need for sensors and regulators as is gen erally required in a heat exchanger used in a refrigeration system. i

The operation of the sublimator may best be explained by considering that the porous member contains a large number of closely packed passages. Each passage may undergo a cycle as follows: beginning with a solid plug of ice in the passage, sublimation occurs at the surface exposed to space and as a result, subcools the walls of the passage. Of course, it is assumed that this device is subjected to outer space or to an extremely low pres-` sure which may be created by evacuating the ambient air. When the thickness of the ice layer formed in the passages is reduced until it can no longer support the internal pressure in the sublimator, water begins to flow through the passage to space. When the liquidwater sees pressure below its triple point and encounters the subcooled passage walls, it freezes, reforming the plug and completing the cycle. Although operation of `a single passage is cyclic, operation of the gross porous plate is continuous. p

We have found that we can provide a complete refrigeration system utilizing this type of sublimator by pumping the refrigerant to cool remote stations intended to be cooled by a pump disposed in a refrigerant closedloop circuit wherein the heated refrigerant rejects heat picked up from various items intended to be cooled in the sublimator. A reservoir containing the refrigerant under pressure adds refrigerant proportionally to the amount depleted as a result of sublimation. Obviously, the refrigerant has to be replenished once the reservoir has completely emptied. Since this system utilizes refrigerant in an optimum manner, a secondary cooling fluid and a secondary heat transfer surface as disclosed in U.S. application 303,382, supra, are eliminated, thus resulting in a simpler, more efficient and lighter cooling system.

It is therefore an object' of this invention to provide a refrigeration system as described, including a sublimator having a porous plate mounted in a closed-loop refrigeration circuit.

Other features and advantages will be apparent from the specification and claims and from the accompanying drawings which illustrate an embodiment of the invention.

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FIG. 1 is a schematic illustrating the principles of this invention.

FIG. 2 isa sectional view illustrating a cylindrical type of sublimator construction.

FIG. 3 is a perspective view illustrating aiat plate type of sublimator construction.

Referring now more particularly to FIG. 1 showing the preferred refrigeration system as comprising a pressurized refrigerant reservoir generally indicated by numeral 12, a sublimator indicated by numeral 14, a pump 16 directing refrigerant to blank box 18 schematically indicating the various items intended to be cooled. The sublimator consists of porous plate 20 which may be formed in a cylinder closed at either end disposed in a chamber subjected'to apressure below the triple point of lthe refrigerant. In an outer space application this chamber may be directly communicating with the outer atmosphere which obviously is at substantially zero pressure. Reservoir 12 is formed into two compartment cylinder separated by suitable resilient means such as diaphragm 24. A gaseous substance is inserted in the chamber 26, acts on the left-hand side of diaphragm 24 and a suitable refrigerant, such as water, is retainedin the chamber 27 on the right of diaphragm 24. Obviously, any suitable mechanical spring may be inserted in chamber 26 to act against diaphragm 24. The pressure exerted by the gases or spring (not shown) acting on the left-hand side of diaphragm 24 forces the refrigerant to chamber 30 defined by porous cylinder member 20, via suitable lines 32 and 34. A portion of this refrigerant migrates toward the outer surface 36 of porous member 20 and freezes by virtue of the low pressure within chamber 38.

Pump 16 as schematically illustrated is disposed in line 40 and serves to direct the refrigerant from chamber 30 to the items intended to be cooled as represented by blank box 18. Of course, it is to be understood that the blank box 18 is illustrative of the items, cabins, compartments, electrical equipment, etc. intended to be kept cooled. i The liquid picking up the heat being rejected by the items illustrated by box 18 is then discharged back into line 34 where it is then redirected into chamber 30 of the sublimator 20 and the cycle is then repeated in a continuous manner.

From the foregoing it is apparent that the refrigerant picking up the heat rejected by the items represented by blank box 18 cools itself in sublimator 20 by coming in contact with the cooler surface of the porous plate and the frozen' water contained therein. The fluid then leaving the sublimator 20 is recirculated to continuously pick up heat as required.

As noted from FIG. 2 the sublimator may comprise an outer wall 50 made from a suitable porous material such as sintered nickel, stainless steel or the like, defining a refrigerant chamber 52. A metal spirally shaped fin 54 in contact with the outer wall S0 is suitably disposed in chamber 52 for agitating the refrigerant therethrough for increased heat transfer and for increasing surface area Contact with the inner surface of outer wall 50. Openings formed at `the ends of outer wall 50 receive suitable connecting ducts 56 and 58 which serve to direct the refrigerant through chamber 52. Ducts S6 and 58 each carry at their outer end suitable connecting means 64 and 66 for receiving suitable ducting or conduits connecting the sublimator to the rest of the system.

Another exemplary showing of a suitable sublimator is illustrated in FIG. 3 as having a top plate 70 and parallelly spaced bottom plates 72 both made from porous material sandwiching a continuous n element 74. Side Walls 76 and 7S abut adjacent opposite edges of iin element 74 and extend between the top and bottom plates defining an open-ended chamber 80 which, by virtue of the continuous fin element, is divided into a plurality of open-ended channels. As phantomly shown, inlet header 82 and outlet header 84 are suitably mounted adjacent the inlet and outlet respectively of chamber 80 for receiving and discharging refrigerant in the manner described in the above.

While sintered metalsuch as nickel andstainless steel have been used successfully as the porous members of the sublimator in laboratory tests, it is contemplated Within the scope of this invention that nonmetal porous members can be used. However, lthe primary requirement of the porousrplate is that it has `a relatively small and uniform pore Vsize in the order of less than 100 microns. The criteria of the pore size is that the porous plate is relatively impervious to the flow of liquid under normal operating pressure and that the migration of the liquid refrigerant from the bottom surface to the top surface is by capillary action.

. An example of a suitable plate is given for illustrative purposes but it is to be understood thatthis invention is not so limited.

(l) The plate is made from 98% pure nickel spherical l or shotted powder.

(2) The plate has an initial point of 3.9 inches-5.3 inches of mercury andan 80% minimum bubble area at 5.3 inches to 8.5 inches of mercury when tested with air under the plate and a 0.20-.040 inch column of methyl alcohol above the plate.

It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be' made without departing from the spirit or scope of this novel concept as defined by the following claims.

1. In combination, a refrigeration system including a sublimator having a porous plate having a surface subjected to refrigerant andV an opposing surface subjectedv to a pressure below the triple point of the refrigerant, said porous plate having a pore size whose magnitude is relatively impervious to the ow of liquid under normal operating pressures but allows the refrigerant tomigrate by capillary action to the outer surface so as to freeze. upon contact with said pressure below the triple point' thereof, passage means interconnecting the sublimator and the environment intended to be cooled for defining a closed-loop circuit and pump means in said passage means for forcing refrigerant through said sublimator and said environment intended to be cooled.

2. The combination as claimed in claim 1 wherein said refrigerant is water.

3. In combination, a refrigeration system including a sublimator having a porous plate having a surface subjected to refrigerant and an opposing surface subjected to a pressure below the triple point of the refrigerant,

said porous plate having a pore size whose magnitude is y 4. In combination, a refrigeration system including a Sublimator having a metallic porous plate having a surface subjected to refrigerant and an opposing surface subjected to a pressure below the triple point of the refrigerant, said porous plate having a pore size in the order of less than 100 microns and whose magnitude is relatively impervious to the ow of liquid under normal operating pressures but allows the refrigerant to migrate by capillary action to the outer surface so as to freeze upon contact with said pressure below the triple point thereof, a source of refrigerant ,passage means interconnecting said source and said sublimator and the environment intended to be cooled for defining a closed-loop circuit and pump means in said passage'means for forcing refrigerant through said sublimator and said environment intended to be cooled.

5. In combination, a refrigeration system including a v sublimator having a pair of parallelly spaced porous plates each having a surface subjected to refrigerant and an opposing surface subjected to a pressure below the triple point of the refrigerant, a continuous fin element sandwiched between said plates, side members extending between said plates and abutting opposing edges of said fin element defining therewith a plurality of open-ended channels, said porous plate having a pore size whose magnitude is relatively impervious to the flow of liquid under normal operating pressures but allows the refrigerant to migrate by capillary action to the outer surface so as to freeze upon contact with said pressure below the triple point thereof, interconnecting means communicating with said open-ended channels interconnecting the environment intended to be cooled for defining a closed-loop circuit for leading refrigerant to and from said sublimator pump means in said interconnecting means for forcing` refrigerant through said sublimator and said environment intended to be cooled, and a self-regulating refrigerant supply source.

6. In combination, a refrigeration system including a sublimator having a cylindrical porous plate defining a hollow tube having a peripheral inner surface subjected to refrigerant and an opposing peripheral outer surface subjected to a pressure below the triple point of the refrigerant, said porous plate having a pore size Whose magnitude is relatively impervious to the flow of liquid under normal operating pressures but allows the refrigerant to migrate by capillary action to the outer surface so as to freeze upon contact with said pressure below the triple point thereof, closure means at ythe end of the porous plate defining therewth a cavity portion for receiving refrigerant, a spirally shaped fin element disposed axially in said cavity portion, conduit means communieating with said cavity portion through openings in said closure means for circulating refrigerant to and from an environment intended to be cooled, and pump means in Said conduit for forcing refrigerant through said conduit means.

References Cited by the Examiner UNITED STATES PATENTS 2,182,788 12/ 39 Cornell 62-315 2,461,636 2/49 Gaylor 62-315 2,908,455 10/59 Headley 62-239 2,990,696 7/61 Fisher 62-314 3,100,386 8/63 Chausson 62--268 3,138,009 6/64 McCreight 62--315 3,170,303 2/65 Rannenberg 62-64 WILLIAM J. WYE, Primary Examiner. 

1. IN COMBINATION, A REFRIGERATION SYSTEM INCLUDING A SUBLIMATOR HAVING A POROUS PLATE HAVING A SURFACE SUBJECTED TO REFRIGERANT AND AN OPPOSING SURFACE SUBJECTED TO A PRESSURE BELOW THE TRIPLE POINT OF THE REFRIGERANT, SAID POROUS PLATE HAVING A PORE SIZE WHOSE MAGNITUDE IS RELATIVELOY IMPERVIOUS TO THE FLOW OF LIQUID UNDER NORMAL OPERATING PRESSURE BUT ALLOWS THE REFRIGERANT TO MIGRATE BY CAPILLARY ACTION TO THE OUTER SURFACE SO AS TO FREEZE 